Tosshinta Tomoe is a high school student who joins his school's judo club to emulate his mother Teruko, a former judo champion. He aims to honor her legacy and meet her demanding expectations. Teruko exerts intense pressure, threatening severe consequences like chopping him "into Tuna" should he fail critical matches, driving his journey through familial pressure.

As a dedicated and strategic judoka, he employs tactics to exhaust opponents, such as sending lower-ranked club members ahead of his own matches. His technical prowess shines through specialized techniques, particularly the "Tomoe Tornado Drop"—a modified Tomoe Nage throw where he uses his foot to swing diagonally, lifting opponents into a spin that hurls both fighters out of bounds. This high-risk maneuver, described as potentially lethal to the user, results in a draw against the protagonist Banji Suke. Despite the outcome, Teruko expresses pride in his courage.

His commitment deepens post-match when Banji joins the judo club out of respect for Tomoe's sacrifice, bolstering the team. This victory is swiftly challenged by another club leader, signaling Tomoe's ongoing role in school conflicts.

In the anime adaptation, his judo challenge against Banji occurs in improvised conditions due to the club's lack of a proper dojo. During the fight, he becomes flustered upon realizing Banji is not wearing a bra, leading to embarrassment. Teruko intervenes, chastising him for shaming the family. Provoked, he executes the "Tomoe Tornado Down Attack," spinning his opponent to build momentum. The technique backfires on non-tatami ground, drilling him into the earth until buried. Teruko rescues him, reinforcing her recurring influence on his endeavors.